Calibrating the data logger…
Declining mule deer (Odocoileus hemionus) populations resulting from apparent low recruitment brought management and political focus on neonatal fawn survival. We captured mule deer fawns on the Uncompahgre Plateau (5,957 km2) in west-central Colorado, USA, at a mean age of 3 days (range = newborn to 6 days), and we radiomarked them with mortality-sensing, drop-off radiocollars. We radiomarked 230 fawns with samples of 50 in 1999, 88 in 2000, and 92 in 2001. Designated neonate survival period was from capture to 14 December. Survival was different among years (χ22 = 6.160, P = 0.046) with 3-year mean survival of 0.501. Cause-specific mortality ordered from highest to lowest was sick/starve, coyote, unknown, trauma, bear, and feline. Neither all predation combined (coyote, bear, feline; P = 0.379) nor coyote predation alone (P > 0.989) differed among years. By 31 July, 74% of the sick/starve mortality and 75% of the predation mortality had taken place, with 76% of mortality from all sources occurring by this date. Mean fawn weights at capture were different among years (P = 0.044). We also found a difference in hind-foot length among years (P = 0.002). Weight and hind-foot means were different between 2000 and 2001 (P > 0.017), with 1999 not different from either 2000 or 2001 (P < 0.017). Mean capture date was 19 June (SD = 4.83 days) and median capture date was 19 June (range = 9 Jun–6 Jul), with 94.8% of all captures occurring between 13 and 30 June. This implies that most does were bred during their first estrus cycle. Neonatal survival through 14 December did not completely account for observed low fawn:doe (f:d) ratios. We hypothesized that fetus mortality during late pregnancy or mortality of fawns at birth (before they could be detected for capture) as potential causes of poor recruitment.
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